A known vehicle door is configured so that a door frame constituting a window frame is fixed to a door body serving as a door panel provided at a vehicle body, the door body being selectively opened and closed relative to the vehicle body. Such door frame includes a vertical portion fixed to an upper end portion of the door body and extending in an upward direction of the vehicle, and a main frame portion connected to an upper edge of the vertical portion and extending in a forward or rearward direction of the vehicle to be connected to the upper end portion of the door body. Such door frame for a vehicle is disclosed in JP2010-105531A, which will be hereinafter referred to as Reference 1.
Particularly in a case where a vehicle is driven at a high speed, a suction force is applied to the vehicle door in an outward direction of the vehicle due to a negative pressure generated by an air flow along the vehicle door. In addition, because the vertical portion is fixed to the upper end portion of the door body while extending in a vertical direction of the vehicle, the vertical portion receives a force to bend in the outward direction of the vehicle by the aforementioned suction force relative to a lower end of the vertical portion serving a fixed end. Therefore, in order to restrain a deformation of the vertical portion caused by the suction force, the vertical portion may be desirably configured so that rigidity thereof is higher at the upper end side than a vicinity of the door body.
Thus, according to the door frame disclosed in Reference 1, an envelope portion (specifically, a wide width vertical wall and a narrow width vertical wall) serving as a main portion of the vertical portion is formed so that a width of the envelope portion in a vehicle width direction gradually increases towards the door body. As a result, the rigidity of the vertical portion is higher in the vicinity of the door body than at the upper end side.
These days a further improvement of rigidity of the door frame may be required. According to configurations of Reference 1, however, the vertical portion may extend or project to an interior space of the vehicle by the increase of the width of the envelope portion in the vehicle width direction. That is, in order to fulfill the required rigidity of the door frame, the interior space may be reduced.
A need thus exists for a door frame for a vehicle which is not susceptible to the drawback mentioned above.